Conventionally, aluminum or an aluminum alloy has generally been used as a wiring material for a display device such as a flat panel display. With upsizing and resolution enhancement of the display, however, such aluminum wiring materials became to raise a problem of signal delay due to the properties thereof such as wiring resistance, causing difficulty in displaying a uniform screen.
While copper (Cu) has an advantage of lower resistance over aluminum (Al), in a case where copper is used for gate wiring, it has a problem of insufficient adhesion between the substrate (for example, a glass substrate) and the copper. In addition, in a case where copper is used for source-drain wiring, there are problems as follows: copper may diffuse into the underlying silicon semiconductor film; copper may be oxidized due to diffusion of oxygen from an oxide semiconductor film; and the like. In order to solve the above-described problems, multilayer-film wiring has been studied in which a copper layer is provided via a barrier film made of a metal having high adhesion to a substrate (for example, a glass substrate) and also having a barrier property that prevents diffusion into a semiconductor film. As metals having both adhesion and a barrier property, metals such as molybdenum (Mo) and titanium (Ti) are known. The multilayer-film wiring employs a two-layer multilayer film in which a layer made of copper and a layer made of such metal or an alloy thereof are laminated, or a three-layer multilayer film in which a layer made of a metal such as molybdenum or titanium or an alloy thereof is further laminated on said copper layer in order to prevent oxidation of the layer made of copper.
Copper- and titanium-containing multilayer-film wiring can be obtained by forming the above-described multilayer film on a substrate (for example, a glass substrate) by a film formation process such as sputtering, and subjecting the resultant to etching using a resist as a mask to form an electrode pattern.
Etching processes include wet etching that uses an etchant and dry etching that uses an etching gas such as plasma. Characteristics such as follows are required for the etchant used for wet etching:                high processing accuracy;        highly stabile and safe components and easy handling;        stable etching performance; and        good wiring configuration should result after etching.        
As an etchant used in the step of etching a copper- and titanium-containing multilayer film, for example, acidic etchants containing hydrogen peroxide, carboxylic acid, carboxylic acid salt or a fluorine compound (Patent Document 1), and acidic etchants containing peroxosulfuric acid salt, an organic acid, ammonium salt, a fluorine compound, a glycol compound or an azole compound (Patent Document 2) are known.
Furthermore, as peroxide-free etchants for copper, an ammonia alkaline etchant containing a copper (II) ion and ammonia, and an acidic etchant containing a copper (II) ion and a halide ion are known. Additionally, as a peroxide-free copper etchant, etchants containing a maleic acid ion source and a copper (II) ion source are also proposed (Patent Document 3).
Moreover, as etchants used in the step of etching a copper- and titanium-containing multilayer film, etchants containing an inorganic salt-containing oxidant, an inorganic acid, and a fluoride ion source are known (Patent Document 4).
However, if an etchant containing hydrogen peroxide or peroxosulfuric acid as Patent Documents 1 and 2 is used, there are problems such as generation of gas and heat due to decomposition of hydrogen peroxide or peroxosulfuric acid, and change in the etching performance due to decomposition of the components.
In addition, although a peroxide-free copper etchant as Patent Document 3 is capable of etching copper, it has difficulty in etching titanium and thus is not appropriate as an etchant used for the step of etching a copper and titanium multilayer film.
When an etchant containing an inorganic salt-containing oxidant, an inorganic acid and a fluoride ion source as Patent Document 4 is used in the step of etching a copper- and titanium-containing multilayer film, the etching time and the wiring configuration were not good (see Comparative Examples 7-9).